Amyloid deposition in the conjunctiva is most commonly a localized idiopathic process seen in healthy young and middle-aged adults. The deposits are typically composed of monoclonal immunoglobulin (AL amyloid) secreted by local clonal plasma cells. Conjunctival amyloidosis may also be induced by long-standing inflammation, as with trachoma (ie, secondary localized amyloidosis, AA amyloid). In rare cases, conjunctival amyloidosis may occur in the setting of primary conjunctival lymphoma or plasmacytoma or secondary to systemic lymphoma or plasma cell myeloma.
Clinically, conjunctival amyloidosis typically presents as a salmon-colored nodular elevation that may be associated with hemorrhage (Fig 5-13A). Histologically, amyloid appears as a glassy pink, extracellular deposit within the stroma, sometimes in a perivascular distribution. On Congo red stain under standard light, amyloid deposits appear red orange. When viewed with polarized light, they exhibit birefringence with dichroism; that is, they change from red orange to apple green (Fig 5-13B–D). Other useful stains include crystal violet and the fluorescent stain thioflavin T.
Figure 5-13 Conjunctival amyloidosis. A, Clinical appearance at the limbus and adjacent bulbar conjunctiva. B, Histologic examination reveals diffuse, amorphous, extracellular eosinophilic material throughout the stroma. C, Congo red stain under standard light stains the amyloid red orange. D, On Congo red stain under polarized light, amyloid exhibits apple-green birefringence (dichroism).
(Parts A, C, and D courtesy of George J. Harocopos, MD; part B courtesy of Shu-Hong Chang, MD.)
Electron microscopy shows characteristic fibrils. Immunohistochemical (IHC) methods, sequencing, and mass spectrometry–based proteomic analysis are some of the techniques used in amyloid subtyping. Mass spectrometry is particularly sensitive.
Excerpted from BCSC 2020-2021 series: Section 4 - Ophthalmic Pathology and Intraocular Tumors. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.